Air conditioning system



May 29, 1956 Filed Feb. 9, 1.953

N. S. SHATALOFF AIR CONDITIONING SYSTEM 2 Sheets-Sheet 1 JVIca/as 6: Sfiahbff BY WM ATTORAE'YS INVENTOR.

May 29, 1956 N. s. SHATALOFF 2,747,842

AIR CONDITIONING SYSTEM Filed Feb. 9, 1953 2 Sheets-Sheet 2 IN VEN TOR.

ATTORNEYS United States Patent 2,747,842 AIR CONDITIONING SYSTEM Nicholas S. Shatalotf, New York, N. Y., assignor to Buensod-Stacey, Incorporated, New York, N. Y., a corporation of Delaware Application February 9, 1953, Serial No. 335,725

9 Claims. (Cl. 257-3) This invention relates to air conditioning systems, especially air conditioning systems which condition a plurality of separate zones.

Air conditioning systems of this type may include central conditioning apparatus, an air distributing unit in each zone, and Warm air and cold air ducts for supplying each air distributing unit with warm and cold conditioned air from said central conditioning apparatus. In such systems, particularly those in which each distributing unit can be individually regulated, the demand for warm air and for cold air frequently varies, thus requiring controls for regulating air supply to the ducts and also requiring reserve capacity in the ducts to make air available immediately when needed. The changing demands cause frequent pressure variations in the warm air duct and cold air duct. Sometimes the pressure in an air duct becomes excessive and unnecessarily wasteful, while at other times the pressure becomes insufiicient to supply the required amount of air to satisfy the demand.

It is an object of this invention to provide an air conditioning system for furnishing conditioned air at substantially constant volumetric rate of delivery to each of a plurality of zones, regardless of variable demands of hot air and cold air in each zone.

Another object of this invention is to provide a simple and highly effective control for hot air and cold air supply ducts of such air conditioning systems for making immediately available increased amounts of conditioned air where necessary without requiring the usual reserve capacity in such supply ducts.

In accordance with this invention, a warm air duct and a cold air duct supply respectively warm and cold air from central conditioning apparatus to individual air mixing and distributing units in a plurality of separate zones to be conditioned. Each unit can be regulated independently of the others, and warm air and cold air may be selectively proportioned in the mixing chamber so that conditioned air is distributed at proper temperatures to satisfy the particular requirements in each zone. The cold air supply duct and warm air supply duct may have approximately the same cross sectional area and normally carry the same amounts of air. However, when more cold air than warm air is demanded of the system, the increased demand for cold air is accompanied by a corresponding decrease in demand for warm air. To meet this condition efiiciently and economically, excess air in the warm air duct is automatically passed through an interconnecting duct to the cold air duct to make up the increased amount demanded. The air is conditioned as it passes through such interconnecting duct in order to lower its temperature to a degree corresponding to that of the air in the cold air duct. Likewise, when there is an increased demand for Warm air,air is automatically passed from the cold air duct through an interconnecting duct to the warm air duct, and is conditioned in such duct in order to raise its temperature to a degree corre- 2,747,842 Patented May 29, 1956 sponding to the temperature of the air in the warm duct.

In the preferred embodiment of this invention, the warm air supply duct and the cold air supply duct are interconnected by two separate ducts, one having a heater therein and the other having a cooler therein. Each interconnecting duct also has a flow control which permits communication between the warm air supply duct and cold air supply duct so that pressure drops across the interconnecting ducts, which result from unbalanced demands of warm air and cold air in the air supply ducts, will induce a flow from one air supply duct to the other. The flow controls in the interconnecting ducts are operative in response to flow from the cold air supply duct to the warm air supply duct to check such flow in the duct with the cooler and to permit free flow through the duct with the heater, and are operative in response to flow from the warm air supply duct to the cold air supply duct to check such flow in the duct with the heater and to permit free flow through the duct with the cooler. By this arrangement, when more warm air is required than cold air, air is transferred from the cold air duct to the warm air duct to satisfy the increased demand, and such air is heated in the transfer duct before entering the warm air duct. Likewise, when more cold air than warm air is required, air is transferred from the warm air supply duct to the cold air supply duct to meet the increased demand, and such air is cooled in the transfer duct before it enters the cold air duct.

In another embodiment of my invention, separate fans are used in the central conditioning apparatus for supplying air to the warm air supply duct and cold air supply duct. Under low loads in this arrangement, one; fan may be turned off, or at least may be set at low speeds, while the other can supply substantially all the conditioned air required of the system by forcing air into one air duct and delivering part of such air into the other duct through an interconnecting duct.

In still another embodiment of the invention, seasonal control of the air flow in a dual duct system as described above is effected by a single interconnecting duct between duct to permit air flow through the interconnecting duct from the warm air supply duct to the cold air supply duct. A cooler is provided in the interconnecting duct to lower the temperature of the warm air flowing to the cold air duct. When the system is set for winter operation, the flow control is operative in response to predetermined excess static pressure in the cold air supply duct to permit airflow through the interconnecting duct from the cold air supply duct to the warm air supply duct. The interconnecting duct is provided with a heater for raising the temperature of the cold air flowing to the warm air duct. The cooler and heater may be operated in coordination with the setting of the system at summer and winter operations. The heater may be thermostatically controlled in response to temperature of the air flowing into warm air supply duct from the cold air supply duct. This thermostat may also be connected to -a reset thermostat in the outside atmosphere so as to this invention will become apparent from the following;

description of the accompanying drawings which are merely exemplary.

In the drawings:

Figure 1 is a schematic view of an air conditioning :system embodying this .invention;

Figure 2 is another embodiment of an air conditioning system according to this invention; and

Figure 3 is a fragmentary sectional view of an interconnecting duct of still another embodiment of this invention, showing schematically different parts of the assembly.

Referring now to Figure 1, central conditioning apparatus, generally indicated at 20, supplies warm and cold conditioned air through warm air supply duct 21 and cold air supply duct 22 to zone control air distributing units 23, for example, units of the construction described in Patent No. 2,620,983, issued December 9, 1952. The units are disposed in several zones to be conditioned, and in each unit warm air and cold air are proportioned and mixed in order to distribute conditioned air at the degree desired in the respective zones. In the event high pressure air is used, these units also act as pressure reducing chambers.

The central conditioning apparatus includes a supply fan 24 for delivering air at a constant volumetric rate into a duct 25, which is bifurcated at 26 so as to form two branches, each of which has approximately the same cross sectional area as the other. One of the branches has a heater 27 at its forward portion near supply fan 24, and forms the warm air supply duct 21. The other branch has a cooler 28 at its forward portion, and forms the cold air supply duct 22.

Flow of heating fluid through coils 29 of heater 27 is regulated by a thermostatically-operated valve V1. In the form shown, the valve V1 may be connected through arelay (not shown) to a thermostat T1 disposed in the warm air duct downstream of such heater for controlling the temperature of air flowing through duct 21. By this construction, warm air can be maintained at desired temperatures by appropriate adjustment of thermostat T1. Likewise, flow of cooling fluid through coils 30 of cooler 28 is regulated by a thermostatically-operated valve V2, which may be connected through a relay (not shown) to a thermostat T2 disposed downstream of the cooler in duct 22 for controlling the temperature of air flowing through duct 22.

Switches S1 and S2 are provided for activating and inactivating themostats T1 and T2, respectively, so that the heater and cooler may be selectively operated only when it is necessary to heat or cool air supplied by the fan.

Branches 31 and branches 32 respectively deliver air from warm air supply duct 21 and cold air supply duct 22 to. zone control air distributing units 23. The end. portions of ducts 21 and 22 remote from fan, 24 are interconnected by duct 34 and also by duct 35. When the pressures in warm air supply duct 21 and cold air supply duct 22 are substantially equal, there is no flow through interconnecting ducts 34 and 35. However, when the pressure in one of the air supply ducts falls as a result of increased air demand in that duct, and pressure inthe other duct increases, as a result of the corresponding decreased air demand in such duct, the resulting pressure drop between the air supply ducts causes air to flow through both interconnecting ducts from the high pressure air supply duct to the lowpressure; air supply duct. In this manner, the increased demand, in one duct is met by air supplied from the other duct in which the demand has fallen. Thus, the pressures in the ducts tend to equalize, and a substantially constant volumetric rate of i ch g is ma n a d in a h. distributin unit.

Duct 34, as shown in Figure I, has, a.v flow control 36 and a heater 37 between such control and Warmair supply duct 21. Flow control 36. normally closes, the

passage, defined by interconnecting duct 34-, but is opera,-

tive in response to flow through duct 34 from cold air supply duct 22 to warm air duct 21 to permit such flow. The flow control will, however, check flow through the duct 34 in the opposite direction; that is, from the warm air supply duct 21 to the cold air supply duct 22. As the cold air passes to the warm air duct through interconnecting duct 34, it is heated by heater 37 in order to raise its temperature to a degree corresponding to that of the air in the warm air supply duct.

In the preferred form, the flow control 36 includes any well-known flap valve, which valve lies in a plane extending transversely across the passage defined by duct 34. Such valve is normally closed and will remain closed when the pressure in the warm air supply duct exceeds that in the cold air supply duct so as to prevent flow of air from the warm air duct to the cold air duct. However, when the pressure in the cold air supply duct exceeds that in the warm air supply duct, the valve will open under such unbalanced pressure to permit free flow of air from the cold air duct to the warm'air duct.

Duct 35 has a flow control 40 and a cooler 41 between such control and cold air duct 22. Flow control 40 has a flap valve similar to those in flow control 36 in duct 34, except that the relative positions of the parts of the valves are reversed. Thus, when the ressure in the cold air supply duct exceeds that in the Warm air supply duct, the flap valve will remain closed so as to check flow of air from the cold duct to the warm duct. The valve is opened in response to flow in the opposite direction from warm air supply duct 21 to cold air supply duct 22 to permit free flow in this direction. Cooler 41 cools the warm air passing from the warm air duct to the cold air duct in order to lower its temperature to a degree corresponding to that of the air in the cold air duct.

Air flowing from the cold air supply duct 22 to the warm air supply duct 21 is maintained at desired temeratures by appropriate adjustment of a thermostat T3, which is connected by a relay (not shown) to a valve V3 for controlling flow of heating fluid through the heater 3']. Likewise, the temperature of the air flowing from the warm air supply duct 21 to the cold air supply duct 22 is controlled by adjustment of thermostat T; which is connected by a relay (not shown) to valve V4 for controlling the flow of a suitable brine solution through cooler 41. Switches S3 and S4. are provided for activat ing and inactivating thermostats T3 and T4, respectively, so that the heater 37 and cooler 41 may be selectively operated.

Summarizing the foregoing, air is supplied by fan 24 to ducts 21 and 22 in which air is respectively heated and cooled by heater 27 and cooler 28; warm air and coldair are then distributed through pipes 31 and 32, respectively to the zone control air distributing units 23. When the system demands the same amounts of warm air and cold air, the pressures in the Warm air supply duct 21 and cold air supply duct 22' are substantially equal. In the event that more warm air is demanded than cold air, the pressure in the warm air supply duct drops and im mediately effects a flow of air into the warm air supply duct 21 from cold air supply duct 22 through interconnecting ducts 34 and 35. As described above, flow control 40 checks such flow in duct 35 so that cold air only flows through interconnecting duct 34 and is heated by heater 37 before it enters the warm air duct. Air will continue to flow through the duct 34 until the pressures.

in air supply ducts 21 and 22 equalize. In a like manner, when more cold air is demanded of the system than. warm air, the increased amount demanded is immediately supplied from the warm air supply duct through interconnecting; duct. 35 because ofv the unbalanced pressure condit-ion effected in the air supply ducts by the unbalanced airdemand. In this case, flow through duct 3.47 is checked by flow control 36 so that warm air flows through duct 35 and is cooled by cooler 41 to lower its temperature to a degree corresponding to that of the air in cold air duct 22.

By this arrangement, minimum diameter or cross sectional area air supply ducts can be used, for this system immediately supplies increased amounts of conditioned air when demanded without the usual reserve capacity which was heretofore necessary. Furthermore, in the operation of this system, a substantially constant pres sure head is maintained in the Warm and cold air supply ducts for any given power setting of the fan, regardless of the warm air and cold air demands made on the system. I

Referring now to Figure 2, a modified arrangement is shown wherein the central conditioning apparatus includes separate fans for each air supply duct. In this embodiment, air is forced through warm air supply duct 21 by a fan 45 which draws air through heater 27 disposed on the suction side of the fan. Another fan 46 forces air through cold air duct 22, the air being initially cooled by cooler 28 disposed on the suction side of the fan. The fans normally deliver equal amounts of air to air supply ducts 21 and 22, and the arrangement is otherwise the same as that of Figure 1. A particular advantage of this arrangement is that during night operation or during other periods of low loading, fan horsepower can be reduced by turning one fan ofi, or at least turning it down low, and by supplying the air required in both ducts by one fan. Either fan may be used to force conditioned air through one of the supply ducts. By the present arrangement, a portion of this air is passed through an interconnecting duct into the other supply duct. If, for example, fan 46 is turned off and fan 45 is operating, air is drawn through heater 27 and forced by fan 45 through warm air duct 21. A portion of the air is delivered to zone air distributing units 23 via branch ducts 31 while the rest is delivered into cold air supply duct 22 through interconnecting duct 35, which has flow control 36 allowing free flow of air therethrough in this direction, and which has cooler 41 for cooling the Warm air before it enters cold air supply duct 22. Air will not flow freely through duct 34 in this direction because flow control 36 checks such flow. If fan 45 is turned off and fan 46 is operating, air is drawn through cooler 28 and forced by fan 46 through cold air supply duct 22. In this case, part of the air is delivered into zone air distributing units 23 via branches 32 while the rest is delivered into warm air supply duct 21 through interconnecting duct 34 in which free flow in this direction is allowed and in which the cold air is heated by heater 37 before it enters warm air supply duct 21 for distribution through branches 31 into zone control air distributing units 23. Air will not flow freely through interconnecting duct 35 from duct 22 to duct 21 because flow control 40 checks such flow.

Referring now to Figure 3, a simplified air flow control is shown for supplying make-up air in response to increased hot and cold air demands in air supply ducts of a dual-duct air conditioning system, which is suitable for operation in accordance with seasonal loads. In this embodiment of the invention, the warm and cold air supply ducts communicate with each other through asingle interconnecting duct 50, and when the system is set for a particular seasonal operation, air is transferred only from one particular duct to the other, for example, during summer operation when cold air demands far exceed warm air demands, air is transferred only from the warm air supply duct to the cold air supply duct in response to increased demands of cold air in the cold air supply duct, and during winter operation, when warm air demands far exceed cold air demands, air is transferred only from the cold air supply duct to the warm air supply duct in response to increased demands of warm air in the warm air supply duct. The term summer operation is defined as operation at relatively warm outside air temperatures, and winter operation is operation at relatively cold outside air temperatures.

Flow from one air supply duct to the other through interconnecting duct 50 is controlled by dampers 51 and 52 disposed respectively at opposite ends of duct 50; Dampers 51 and 52 are normally closed, but are opened by static pressure regulators 53 and 54 in response to predetermined pressure difference in air supply ducts 21 and 22. The regulators are activated and inactivated by a master switch 55 in accordance with seasonal demands. Switch 55 may be hand-operated, or may be automatically operated in response to the temperature of the outside atmosphere. The regulators 53 and 54 are respectively connected with the dampers 51 and 52 by suitable relays 56 and 57; each regulator has a pressure responsive member 58 disposed in the warm air supply duct 21 and a pressure responsive member 59 disposed in the cold air supply duct 22.

When the switch 55 is set for summer operation, static pressure regulator 53 is activated, whereas static pressure regulator 54 is inactivated. In the event that a substantial increase of cold air is demanded of the system, and the static pressure in the warm air supply duct exceeds that in the cold air supply duct by a predetermined amount, the pressure regulator 53 will operate in response to such predetermined pressure difference so as to open dampers 51 and 52 and allow air to flow from the warm air supply duct 21 to the cold air supply duct 22. Air transferred from the warm air supply duct 21 to the cold air supply duct 22 is passed through a cooler 60 disposed in the interconnecting duct 50 in order to lower the temperature of such air to a degree corresponding to that of the air in the cold air duct.

correspondingly, when the switch 55 is set for winter operation, the static pressure regulator 54 is activated and the static pressure regulator 53 is inactivated. Under this setting the dampers 51 and 52 remain closed unless the static pressure in the cold air duct 22 exceeds that in the warm air duct 21 by a predetermined amount, which condition will occur when the demand for warm air exceeds that for cold air by a predetermined amount. When this condition occurs, static pressure regulator 54 operates in response to such predetermined pressure difference in the air supply ducts so as to open dampers 51 and 52 and allow air to flow from cold air supply duct 22 to warm air supply duct 21. Air transferred from the cold air supply duct to the warm air supply duct is passed through a heater 61 disposed in duct 50 in order to heat such air before it enters the Warm air supply duct.

The coils of cooler 60 and heater 61 project inwardly from opposite walls of the duct 50 but do not extend across the entire width of the passage defined by duct 50. Flap valves 62 and 63 are respectively disposed in the space between the inner ends of the cooler and heater coils and the adjoining walls of the duct 50; flap valve 62 permitting flow from the cold to the warm air supply duct and checking flow in the opposite direction, and flap valve 63 permitting flow from the warm air supply duct to the cold air supply duct and checking flow in the opposite direction. Accordingly, air passing through duct 50 from the warm air duct 21 to the cold air duct 22 will pass through flap valves 63 and through the cooling coils of the cooler 60, thereby by-passing the coils of the heater 61. Flow in the opposite direction is through flap valves 62 and the heating coils of the heater 61 so as to by-pass the coils of the cooler 60. By this construction friction losses through the interconnecting duct are minimized, for losses which could otherwise occur in passing air through both the heater and the cooler coils are avoided. A conventional spray 64 supplied with Water by circulating pump 65 is provided in duct 50 for washing the coils of cooler 60.

Flow of heating fluid through the coils of the heater is regulated by a thermostatically-operated valve 66, which; is connected by a suitable pressure relay to a thermostat 67 disposed in duct 50 between the heater 61 and the warm air supply duct 21. Thermostat 67 is connected with switch'54, and is activated by this switch when the system is set for winter operation. The temperature of. the air entering the Warm air supply duct through duct.- 50 may be automatically adjusted in accordance withv outdoor temperatures. This adjustment may be effected. by connecting thermostat 67 with a master thermostat 68, which is suitably located in the outside atmosphere. Iri this way, the master thermostat 68 will automatically reset thermostat 67 in accordance with outside air temperature so that the air entering the warm air supply duct will be maintained at a prearranged schedule of temperatures relative to outside air temperatures.

It is to be understood that the detailed description and the accompanying drawings are illustrative and that the invention herein disclosed may be embodied in various forms of construction Within the scope of the appended claims, as Will become apparent to those skilled in the art.

What is claimed is:

1. In an air conditioning system the combination including centrally located air conditioning means, air distributing means in at least one zone to be conditioned, cold air and Warm air supply ducts connecting said central conditioning means with said air distributing means for supplying cold and warm air thereto, means normally forcing air through both of said ducts at substantially the same pressures, and means responsive to increased air demands in one air supply duct for passing air from? the other air duct into said one air supply duct, said last mentioned means including interconnecting duct means between said air supply ducts and other conditioning means in said interconnecting duct means for further conditioning air passed from said other duct to said one duct.

2. In an air conditioning system for conditioning a plurality of separate zones, the combination including centrally located air conditioning means, air distributing means in each zone, cold air and warm air supply ducts connecting said central conditioning means with said air distributing means for supplying cold and warm air thereto, meansnormally forcing air through both of said air supply ducts at substantially the same pressures, interconnecting duct means between said air supply ducts, air flow control means in said interconnecting duct means operative in response to'excess air pressures in one of said air supply ducts, resulting from excess air demands in the other air supply duct, for permitting air flow through said interconnecting duct means from said one. air supply duct to the other air supply duct 56 as to maintain the'pressures in said air supply ducts'substantially constant and-to makeup" the increased air demand in said other air supply'duct; and'other' conditioning means in said interconnecting duct means for further conditioning air passed from said one duct to'the other.

3. In an air conditioning system" for conditioning a plurality of separatezone's', the combination including centrally locatedair conditioning means, air distributing means ineach Zone, cold air and warm air supply ducts connecting said central con'ditioning'means with said air distributing means for supplying cold and warm air thereto, means normally forcing air through both of said air supply ducts at substantially the same pressures, interconnecting duct means between said air supply ducts, air flow control meansinsaid interconnecting duct means operative in response to excess air pressures in one of said air supply ducts, resulting froni'exc'ess air demands in the other air supply duct; for permitting air flow through said interconnecting duct'frornsai'd one air supply duct to the other air supply duetmeans so as to maintain the pressures in said air supply"ducts' substantially constant and to makeup the in'creasedair demand in said other air supply =duct, other conditioning meansin" said inte'r connecting duct means for further conditioning air passed fromsaid one' duct to tlie othei'; and thermostatically & controlled means responsive to temperature of air leaving said other conditioning means for regulating the conditioning effect of such other conditioning means.

4. In an air conditioning system for conditioning a plurality of separate zones, the combination including centrally located air conditioning means, air distributing means in each zone, cold air and Warm air supply ducts connecting said central conditioning means with said air distributing means for supplying cold and warm air thereto, separate means in each air supply duct normally forcing air through these air supply ducts at substantially the same pressures, interconnecting duct means between said air supply ducts, air fiow control means in said interconnecting duct means operative in response to excess air pressures in one of said air supply ducts for permitting air flow through said interconnecting duct means from said one air supply duct to the other air supply duct so as to maintain the pressures in said air supply ducts substantially constant and to make up the increased air demand in said other air supply duct, and other conditioning means in said interconnecting duct means for further conditioning air passed from said one duct to the other.

5. In an air conditioning system for conditioning a plurality of separate zones, the combination including centrally located air conditioning means, air distributing means in each zone, cold air and warm air supply ducts connecting said central conditioning means with said air distributing means for supplying warm and cold air thereto, means normally forcing air through both of said air supply ducts at substantially the same pressures, a pair of interconnecting ducts between said air supply ducts, one of said interconnecting ducts having a heater therein and the other interconnecting duct having a cooler therein, one-way flow control means in said one interconnecting duct normally closing such duct but opening in response to' increased warm air demands for permitting air to flow from said cold air supply duct through the heater to the Warm air supply duct, and one-way flow control means in said other interconnecting duct normally closing such duct but opening in' response to increased cold air demands for permitting air to flow from the warm air supply duct through the cooler to the cold air supply duct.

6. In an air conditioning system for conditioning a plurality of separate zones, the combination including centrally located air conditioning means, air distributing means in each zone, cold air and Warm air supply ducts connecting said central conditioning apparatus with said air distributing means for supplying warm and cold air thereto, means normally forcing air through both of said air supply ducts at substantially the same pressures, an interconnecting duct between said air supply ducts, air flow control means normally closing said interconnecting duct, actuating means responsive to predetermined excess pressure in said warm air supply duct for opening said air flow control means to permit air flow from said warm air supply duct to said cold air supplyduct, other actuating means responsive to predetermined excess pressure in said cold air supply duct for opening said air flow control means to permit air flow from said cold air supply duct to said warm air supply duct, and means for energizing and deenergizing each of said actuating means.

7. In an air conditioning system for conditioning a plurality of separate zones, the combination including centrally located air conditioning means, air distributing means in each zone, cold air and warm air supply ducts connecting said central conditioning apparatus with said air distributing meansfor supplying warm and cold air thereto, means normally forcing air through both of said air supply ducts at substantially the same pressures, an interconnecting duct between said air supply ducts having heating means and-cooling means therein, damper means nor'mhllyblosihgsaid interconnecting'duct, damper actuating means responsive to predetermined excess pressure in said warm air supply duct for opening'said damper means to permit air flow from said warm air supply duct to said cold air supply duct, other damper actuating means responsive to predetermined excess pressure in said cold air supply duct for opening said damper means to permit air fiow from the cold air supply duct to said warm air supply duct, and means for selectively energizing and deenergizing each damper actuating means in accordance with seasonal requirements.

8. In an air conditioning system for conditioning a plurality of separate zones, the combination including centrally located air conditioning means, air distributing means in each zone, cold air and warm air supply ducts connecting said central conditioning apparatus with said air distributing means for supplying warm and cold air thereto, means normally forcing air through both of said air supply ducts at substantially the same pressures, an interconnecting duct between said air supply ducts having heating means and cooling means therein, thermostat control means in said interconnecting duct responsive to temperature of air entering the warm air supply duct and connected with said heating means, an outside air temperature responsive thermostat connected with said thermostat control means for resetting such thermostat, damper means normally closing said interconnecting duct, damper actuating means responsive to predetermined excess pressure in said warm air supply duct for opening said damper means to permit air flow from said warm air supply duct to said cold air supply duct, other damper actuating means responsive to predetermined excess pressure in said cold air supply duct for opening said damper means to permit air flow from the cold air supply duct to said warm air supply duct, and means for selectively energizing and deenergizing each damper actuating means in accordance with seasonal requirements.

9. In an air conditioning system for conditioning a plurality of separate zones, the combination including centrally located air conditioning means, air distributing means in each zone, cold air and warm air supply duets connecting said central conditioning apparatus with said air distributing means for supplying warm and cold air thereto, means normally forcing air through both of said air supply ducts at substantially the same pressures, an interconnecting duct between said air supply ducts having heating means and cooling means therein, damper means normally closing said interconnecting duct, damper actuating means responsive to predetermined excess pressure in said warm air supply duct for opening said damper means to permit air fiow from said warm air supply duct to said cold air supply duct, other damper actuating means responsive to predetermined excess pressure in said cold air supply duct for opening said damper means to permit air flow from the cold air supply duct to said warm air supply duct, means for selectively energizing and deenergizing each damper actuating means in accordance with seasonal requirements, by-pass means associated with said interconnecting duct for passing air flowing through the heating means around said cooling means and for passing air flowing through the cooling means around said heating means.

References Cited in the file of this patent UNITED STATES PATENTS 1,247,374 Chubb Nov. 20, 1917 2,440,052 Lingen et al Apr. 20, 1948 2,609,183 Fitzgerald Sept. 2, 1952 2,609,743 Ashley et al. Sept. 9, 1952 

